Summary:Allogeneic and autologous peripheral blood stem cell transplants are frequently complicated by infections. This study was performed to evaluate early and late infections in 74 patients who underwent peripheral blood stem cell transplantation (PBSCT). Fifty-eight patients received allogeneic and 16 autologous PBSCT. All patients received fluconazole, ciprofloxacin and acyclovir prophylaxis. 93.1% of alloPBSCT patients and 87.5% of autoPBSCT patients developed fever. Febrile episodes were commonly seen in the week of transplantation (66%). There was a median of 3 days with fever in alloPBSCT, and 2 days in autoPBSCT. Period of neutropenia was 15 days for AlloPBSCT and 12 days for AutoPBSCT. The microbiological identification rate was 47% (32/68). Gram-positive infections dominated the early period (50%) and Gram-negative bacterial infections dominated the late period (50%). All our patients had Hickman-type catheters and 26 infections involving catheters were seen. Sixteen occurred in the early, and 10 in the late period. Ten of 14 (71.4%) late bacterial infections were catheter-related. The dominance of Gram-positive infections and high rates of methicillin resistance warranted the use of vancomycin extensively. Surveillance cultures were found to be useful in selected patients. Although slime factor is an important virulence factor, there was no difference between slime factor positive and negative coagulasenegative staphylococci isolated during infections. In conclusion, febrile episodes are the most frequent complication of PBSCT and Gram-positive microorganisms remain the main pathogen in these patients because of catheter use, mucositis and ciprofloxacin prophylaxis. Methicillin resistance is increasing and glycopeptides remain the only choice for treating such infections. Although the infection rate is high, measures taken to prevent and treat infections result in very low rates of mortality from infection in PBSCT patients. Bone Marrow Transplantation (2001) 27, 201-205.